1. Technical Field
The present invention relates to the detection of errors in the location of containers in a container shipping yard. More particularly, the present invention relates to the detection of inventory data errors in inventory tracking databases and/or systems indicating the location of the containers.
2. Related Art
Over the past decade, shipping container handling volumes have been increasing dramatically. Such increases in handling volume are adversely affecting real-time order visibility. Every partner to the transactions needs to have access to location information throughout a container's journey. However, in port, containers are routinely not visible to the consignees.
Operations on a shipping container generally include out-gate operations, in-gate operations, and yard operations. These operations are conducted by people including a yard clerk, an operator of transport equipment, and an operator of lift equipment. The transport equipment (or yard tractor) refers to any type of handling equipment (HE) that is capable of moving a container from one location to another but is not capable of lifting the container and setting it down. The lift equipment refers to any type of HE that is capable of lifting a container and setting it down on the ground, on top of another container, or onto another HE for transportation. For convenience herein, the term yard tractor and container handling equipment (CHE) will be used to refer to transport equipment and lift equipment, respectively. Among the operations performed, yard operations (operations in a shipping container yard) are the most time consuming in overall average transactions. Traditionally during yard operations, a yard clerk must accompany the CHE operator to validate the correct container for pick-up. If the container is not where it is supposed to be, the typical yard clerk wanders around the yard looking for it. When the yard clerk finds it, both the yard tractor driver and the CHE operator who picks up and loads the container onto the yard tractor must be radioed to come to the new location. Even so, the right container might be buried by others that need to be moved out of the way by the CHE operator, all while the yard clerk and yard tractor driver are waiting. It would be more efficient if the CHE operator could have the container free to load and in a verified location by the time the yard tractor arrives.
To improve the efficiency of container terminals material handling processes, inventory tracking systems have been developed to track and monitor what really takes place in the yard. Such inventory tracking systems typically employ both real-time positioning technology (such as RFID, GPS, and radio beacons) and wireless communication technologies. These systems enable active tracking of the location of the containers (typically by tracking the movement and location of the various pieces of HE that move the containers), report the tracking information to an inventory tracking database, and interface with a Terminal Operating System (TOS) to update container locations whenever an HE picks up or sets down a container. These inventory tracking systems target to improve the accuracy of the container yard inventory and thereby reduce lost containers, maximize TOS performance, and improve the efficiency of HEs.
Ideally, if the real-time positioning systems can achieve 100% positioning accuracy and if the wireless communication system has zero loss and noise, the inventory tracking systems could indeed achieve 100% accuracy in container inventory locations. However, in reality, inventory errors occur due to sensor biases and noise, communication loss and errors, as well as component or system faults and operational errors.
The prior art inventory tracking systems employ a traditional approach in error handling that relies heavily on operators of HEs to detect and report errors as well as error types. When a CHE operator receives a task (from the TOS through its interface with the inventory tracking system) with a pickup location (sometimes called source location), a container ID, and a drop location (i.e., target location), he drives the CHE to the pickup location to pick up the specified container and then drives to the drop location to place the container at the drop location. The prior art inventory tracking system compares the actual pickup location with the specified pickup location, and the actual drop location with the specified drop location; if there is a discrepancy, the system warns the driver and the driver has to report the error unless the driver made a mistake during the operation. Other than that, it is up to the driver to report errors as he tries to carry out the operation.
For example, if there is no such container at the specified pickup location or the CHE cannot get to the pickup location due to obstructions, the CHE operator needs to report the error using the user interface installed in the CHE and the system will then cancel the task and go to the next task. If the specified container is actually located in a neighboring location, e.g., located beneath the specified pickup location with containers on top of it (containers are typically stacked on top of one another), the CHE operator has to pick the container up at the actual pickup location, which is different from the specified pickup location. Since the system compares the actual pickup location with the pickup location specified in the task and issues a warning if they are different, the CHE operator will receive a warning and has to report the error to clear the warning signal. When the CHE operator carries a container to the drop location and the drop location is already occupied, the CHE operator has to report the error and request the system to re-determine the drop location. On the other hand, if there is no container immediately under the drop location as specified in drop location instructions, the CHE operator will have to drop the container at a location lower than the specified drop location, which will trigger the system to warn the driver of incorrect operation. In this case, the CHE operator must report the error again.
Such a traditional manual-heavy approach employed by the prior art has several drawbacks. First, since the system only concerns itself with the pickup and drop locations, the types of errors detected are limited. Second, inventory errors can only be detected when the system comes to assign a task that involves an incorrect inventory record; consequently, inventory errors can propagate without detection and can cause erroneous reporting of neighboring inventories. Third, this approach requires CHE operators' input for error detection, which creates additional workload for CHE operators, slows down their operations, and wastes precious resources in terms of both CHEs' and CHE operators' time. Fourth, human beings can make mistakes and this approach is vulnerable to errors in CHE operators' inputs. Consequently, CHE operators must input additional information for error correction, or additional personnel must go to the reported locations for manual error correction.